ENTRAINER SELECTION FOR SEPARATION OF AZEOTROPIC MIXTURES BY DISTILLATION METHODS

Luot Tien Thi

Abstract

Azeotropic or close – boiling mixtures often preclude conventional distillation as a method of separation. Instead, extractive or azeotropic distillations are commonly used to separate azeotropic or close – boiling mixtures. For the design of those separation units, selecting suitable entrainers (solvents) is a key step. The traditional method for solving this problem is to use experimentation which is time – consuming and expensive. Currently available selection criteria are inadequate. They contradict one another and often lead to incorrect conclusions. Indeed, for a minimum boiling azeotrope, the existing entrainer selection rules state that one should use a high boiling component that introduces no additional azeotrope (Benedict & Rubin, 1945), an intermediate boiling component that introduces no additional azeotrope (Hoffman, 1964), a component which introduces no distillation boundary between the azeotropic constituents (Doherty & Caldarola, 1985), and either a low boiling component that introduces no additional azeotrope or a component that introduces new minimum boiling azeotrope (Stichlmaric, Fair & Bravo, 1989).

In this work, Aspen Plus simulator was used to propose an entrainer selection procedure based on the criteria: 1) A good entrainer is a component that eliminates the azeotrope easily (i.e. even when it’s concentration is small). 2) A component that yields high relative volatilities αAB between the two azeotrope constituents.